The instant invention pertains to apparatus for controlling a brake on a drawworks and more particularly to such apparatus which incorporates a fluidic ram for moving a brake handle on the drawworks.
In the drilling of oil and gas wells, a block-and-tackle arrangement is used for suspending a drill string therefrom. The block-and-tackle arrangement is used to raise and lower the drill string into and out of the well bore. A large winch, known as the drawworks, is used to pay out and reel in the cable in the block-and-tackle arrangement for raising and lowering the drill string.
During drilling, the drawworks is stopped at a selected position so that a drill bit suspended from the lower end of the drill string is at the bottom of the hole. A rotary table on the drilling rig imparts rotary motion to the drill string thereby causing additional downward drilling in the bore. It can be seen that as drilling progresses, the weight of the drill string bearing down on the drill bit decreases. The drawworks is equipped with a brake which locks it into position. The brake includes a handle which extends outwardly from the drawworks. When the handle is raised, the brake is released thereby permitting additional cable to be paid out and thus increasing the weight of the drill string on the bit. As drilling further proceeds, the weight of the drill string on the bit again lessens thus requiring deactivation of the brake to again increase the weight of the drill string on the bit.
In the past, several types of apparatus have been proposed for monitoring the drilling operation and for deactivating the brake when appropriate. Such past apparatus generally include a tension gauge for detecting tension in the drawworks cable, such tension being inversely proportional to the weight of the drill string on the bit. A fluidic ram is attached to the brake handle for deactivating the brake responsive to ram movement. Control circuitry monitors the detected cable tension and switches a source of compressed air for moving the ram when the tension is above a preselected level.
Such past apparatus suffer from several deficiencies. Some such apparatus monitor the tension and continuously adjust the brake in response to the varying tension. This leads to a condition wherein the brake may assume a position partway between being activated and deactivated. This may permit hard-to-control slippage and causes excessive brake wear. Although one past apparatus provides for switching of the brake between being activated and deactivated, it includes a complex control circuit and poses a safety hazard. Most past apparatus are limited to drilling under 100 feet per hour.
It is a general object of the instant invention to overcome the above-enumerated deficiencies inherent in past brake control apparatus.
It is a more specific object of the instant invention to provide such apparatus having increased safety.
It is another specific object of the invention to provide such apparatus which is relatively simple in construction and easy to maintain.
It is yet another specific object of the invention to provide such apparatus which includes a control for operator-controlled brake deactivation without removing the fluidic ram.
It is still another specific object of the invention to provide such apparatus which both maintains the brake in an activated condition and disengages the drawworks clutch when the tension in the cable falls below a preselected level.
It is a further specific object of the invention to provide such apparatus which permits drilling at rates in excess of 250 feet per hour.
The instant invention includes a gauge for sensing the tension level in a drawworks cable. A ram is mounted on the drawworks brake handle for deactivating the brake responsive to ram movement. A first pneumatic relay is connected to the ram for deactivating the brake responsive to relay energization. A pulse generator is connected to the first pneumatic relay for pulsing the same when the tension in the cable is above a preselected level. A second pneumatic relay is connected to the ram for maintaining the brake in an activated condition when the cable tension falls below a preselected level and for disengaging a clutch in the drawworks. A switch-operated third pneumatic relay is connected to the ram for switch-controlled brake deactivation.